Dental caries is an infectious and transmissible disease worldwide. This disease is multifactorial and complex;however the basic concepts of the host/parasite relationship are important to pathogenesis. Although various bacteria are involved in the disease process, the mutans streptococci (MS) are most consistently implicated in the initiation of caries in humans. Observations in infants indicate that the initial colonization of the oral cavity with MS occurs with eruption of the primary teeth. The normal source of the initial MS infection in young children appears to be vertical transmission from the mother;however, horizontal transmission may also occur from other family members, caretakers or playmates. In addition to the natural history of infection and availability of colonization sites as well as dietary sucrose intake, there is data to indicate that the development of the host's immunity to MS is also involved in MS colonization. Caries in the primary dentition often corresponds with subsequent higher risk for caries in permanent teeth. Therefore, it is necessary to better define important characteristics of MS infections regarding their clonal development and temporal stability within dental plaque biofilms in humans. The purpose of the studies proposed is to investigate the host/parasite relationship important in the pathogenesis and epidemiology of dental caries in a stable and cooperative high caries risk population of families and children of two age groups corresponding with important tooth eruption events (i.e., primary and permanent molar teeth) associated with caries. This proposal utilizes the latest technologies including polymerase chain reaction and pulsed-field gel electrophoresis to establish the commonality of MS genotypes and stability in a defined population of children and family members. An interdisciplinary team of physicians, dentists, basic scientists, epidemiologists and statisticians has been assembled to improve our understanding of the host-parasite relationship of dental caries in children. The results of these studies should provide key information for the development of strategies to prevent this infectious disease. Additionally, the initiation of these studies in Uniontown, Alabama that is in a "Black Belt" county will provide much needed preventive oral care to children and their household family members and will partner with the Alabama Department of Public Health to arrange necessary dental care to improve oral health in this underserved population.